1. Field of the Invention
The present invention pertains to compositions that are able to provide an abrasion-resistant, dye-tintable coating on a thermoplastic or thermoset polymeric substrate, such as an ophthalmic lens.
2. Background of the Art
It is known that transparent plastic materials such as polycarbonate ophthalmic lenses or screen face plates are subject to becoming dull and hazy due to scratching and abrasion during use.
Attempts have been made to overcome this problem. The technical solutions proposed in the past, which involved applying a UV-curable coating, generally used an organic or aqueous solvent-borne composition which was usually substrate-dependent. That is, the coating compositions were formulated for one specific ophthalmic lens material such as CR-39 (an allyl diglycol carbonate) or thermoplastics such as polycarbonate. The few compositions found in the literature that were solvent-free or substantially organic solvent-free were substrate-dependent. They also usually contained a partially hydrolyzed or fully hydrolyzed silane used both for adhesion and for abrasion resistance.
Moreover, coatings for ophthalmic lenses should also be capable of being tinted by incorporating a dye therein. However, abrasion and scratch resistance, on the one hand, and tintability, on the other hand, are often regarded as hardly parallel properties. Among the solutions proposed to reconcile these properties, U.S. Pat. No. 5,614,321 suggests a curable coating composition comprising colloidal silica, together with a (meth)acrylate compound capable of reacting with said silica, a monomer (preferably an alkoxysilane) bearing (meth)acryloxy groups, a free radical initiator and an organic tintability additive.
US 2002/0193479 teaches a composition comprising both a hydrolyzed and a non-hydrolyzed epoxy-functional alkoxy silane, together with a curing agent and an acrylic monomer preferably bearing not more than two acrylic functions.
Similarly U.S. Pat. No. 6,100,313 (Treadway) discloses a composition comprising an epoxy-functional alkoxysilane, a glycidyl ether, a cationic photoinitiator, an acrylic monomer and a free-radical photoinitiator. It is purported to be solvent-free, but an analysis of the carrier materials and solvents in photoinitiators added indicate a significantly high level or organic solvents.
U.S. Pat. No. 8,033,663 (Valeri) discloses a curable coating composition includes: a) at least one monomer chosen from polyol poly(meth)acrylate monomers having from 3 to 6 (meth)acrylate functions, b) at least one monomer chosen from polyol polyglycidyl ethers having at least three epoxy functions, c) at least one difunctional monomer, d) at least one free-radical photoinitiator, and e) at least one cationic photo-initiator, wherein the molar ratio of acrylate equivalents to epoxy equivalents in the composition ranges from 3:1 to 4:1, and wherein the composition is free of silica and of monomers bearing a silane function. The patent discloses a method for coating a substrate, such as an ophthalmic lens, with this composition, and the coating substrate thus obtained. It is asserted that the coating composition is more stable than the alkoxysilane compositions. However, acryolyl curable compositions are also moisture-sensitive and can produce less abrasive compositions if moisture is introduced into the reaction mixture, even from the air.
It is difficult to find rapidly curing compositions that are relatively stable in a pot during coating operations, provide good abrasion resistance, and then remain dye-tintable, e.g., exhibiting less than 15% transmission to white light after immersion for 15-20 minutes at 90-100° C. in an approximately 5% by weight aqueous solution of a black azo dye such as azo dye Sudan black:
or an anthroquinone dye such as Alizarin blue-black (further identified as CAS Number 1324-21-6 Molecular Formula C26H16N2O9S2Na2, Molecular Weight 610.5, Color Index 63615, EC Number 215-366-9).
BFI Black, manufactured by Brainpower, Inc. of Miami, Fla. has become a standard black tint dye in the ophthalmic industry and would be preferably used for the tint test.
To perform a tinted coating, the surface of the substrate coated with the cured resin matrix of the invention is contacted by a suitable colored dye, in many instances, any commercially viable method of applying the dye may be utilized. The leading manufacturer of suitable dyes is Brainpower, Inc. (BPI) and the usual procedure in tinting follows BPI instructions. In a typical tinting operation the surface of a substrate coated with a cured coating of the present invention is immersed in a heated aqueous dye bath (typically between 90-100° C., usually between 92-98° C.) containing a suitable colored dye, e.g., BPI Sun Black, a molecular catalytic dye sold by BPI of Miami, Fla. The dye solution may be prepared by diluting one part of BPI dye concentration to ten parts water, and then heating the resulting solution to a temperature in the range of about 190° to 212° F. while constantly stirring the solution. The coated surface of the substrate is preferably cleaned by wiping with a compatible solvent prior to immersion in the dye bath at about 90-100° C. for a period of time sufficient to absorb or transmit the desired amount of dye (typically 15-20 minutes), then washed with tap water to remove the excess dye and blown dry with nitrogen. The intensity of the tint can be adjusted by varying the concentration of any organic tintability additive in the coating composition, the thickness of the coating, the time of immersion, or the thickness of the coating. The degree of tint obtained can be determined by using a calorimeter, such as a Gardner XL-835 colorimeter, which measures the percent of light transmittance.
Tintability Test
The percent light transmittance of the samples was determined using a Gardner Haze Meter Model 835 colorimeter with a wavelength range of 600 nanometers. Lexan® (polycarbonate from General Electric Company, Schenectady, N.Y. or any commercial CR-39 polycarbonate), was used as a reference sample and substrate. The percent light transmittance of the uncoated polycarbonate is about 86.9%. The coating compositions were applied to the polycarbonate or other substrate and the percent light transmittance was determined as a direct reading from the meter. For tinted samples, the coated sample was immersed in the dye bath rinsed in cold tap water and blown dry with nitrogen. The formulations of the comparative examples were coated on panels, cured and the coated panels immersed in a 9% tint bath (BPI Black) maintained at 90-100° C. for 15 minutes. The process may also be used with some photochromic dyes including spiro-naphthoxazines, naphthopyrans, anthraquinones, phthalocyanines, spiro-oxazines, chromenes, pyrans, fulgicides and mixtures thereof. Reversacol™ photochromic dyes are available from James Robinson Ltd. (UK) and several of these dyes are listed in the examples below. Permanent dyes can be any permanent dye. Preferred permanent dyes are those that are soluble in the curable material. Permanent dyes include BPI dyes from Brain Power, Inc. (USA) such as BPI Gray and BPI Black. Sigma Aldrich offers a line of permanent dyes such as Solvent Blue, Solvent Black, Solvent Yellow, Solvent Red and Solvent Orange dyes. Preferred dyes include Solvent Black 3, Solvent Black 5, Solvent Black 7, Solvent Blue 43, Solvent Blue 35, Solvent Blue 59, Solvent Blue 14, Solvent Blue 37, Solvent Green 3 and Solvent Red 24. A particularly preferred dye is Solvent Blue 35.
When adding the dye to the curable material (to mask the slight yellow color that some polymers exhibit), a purple or blue dye may be added to the curable material in amounts to mask the yellowness but also in amounts that do not turn the polymer a noticeable blue. A neutral color is desired. In the case of dyes (such as black tinting dyes or Solvent Blue 35 dye) a suitable amount of dye in the curable material is from about 0.0007 wt % to about 0.0020 wt % and preferably from about 0.0010 wt % to about 0.0015 wt % of the total coating. A particularly preferred amount of dye in the curable material is about 0.0008-0.0015%, such as 0.0012 wt %. When adding the dye for tinting for use as sunglasses then the dyes are also added in amounts that aesthetically or cosmetically desirable. Typical classes of dyes include:
Chemical classC.I. Constitution numbersMonoazo 1000-19999Azine50000-50999Disazo20000-29999Oxazine51000-51999Triazo30000-34999Thiazine52000-52999Polyazo35000-36999Sulphur53000-54999
It is believed that within these classes, Disazo, and Triazo dyes are preferred. Other dyes that have been considered are those typically used as dye classes for fibers.
Dye classFiber typeFixation degree,% Loss in effluentAcidPolyamide80-95 5-20BasicAcrylic95-1000-5 DirectCellulose0-955-30DispersePolyester90-1000-10Metal complexWool0-982-10ReactiveCellulose50-90 10-50 SulphurCellulose60-90 10-40 Dye-stuffCellulose80-95 5-20